The technical advancement and increasing demands for mobile devices have led into rapidly increasing demand for the secondary batteries for use as the energy source, and accordingly, numerous studies are under way about batteries that can meet a variety of demands.
For representative example, in terms of the shape of batteries, prismatic batteries or pouch-shaped batteries, which are thin enough to be applied to products such as mobile phones, are in mat demand. In terms of the material for batteries, demand is high for the lithium secondary batteries such as lithium cobalt polymer batteries that exhibit high energy density, discharge voltage and output stability.
One of the main objectives of these researches for such secondary batteries is the safety enhancement. Generally, the lithium secondary battery has a risk of battery explosion due to high temperature and high pressure therein which can be caused by abnormal operating states such as internal short circuit, over-charging state exceeding allowable current and voltage, exposure to high temperature, impact from falling, and so on. One example of such cases is the possibility that the secondary battery is subject to internal short circuit in the event of impact such as falling or application of external force, and so on.
FIG. 1 schematically illustrates a general structure of a pouch-shaped secondary battery.
Referring to FIG. 1, a secondary battery 10 includes an electrode assembly 100, a battery case 200, electrode tabs 10, 11, and electrode leads 20, 21.
The electrode assembly 100 includes a positive electrode plate, a negative electrode plate, and a separator. In the electrode assembly 100, the positive electrode plate and the negative electrode plate interposed by the separator may be sequentially stacked on one another. Representative examples of the electrode assembly 100 may include a jelly-roll (wound type) electrode assembly having a structure in which elongated sheet types of positive electrodes and negative electrodes interposed by the separators are wound, a stack type electrode assembly in which a plurality of positive electrodes and negative electrodes each being cut into a predetermined size unit and interposed by the separators are sequentially stacked, a stack/folding type electrode assembly having a structure in which bi-cells or full cells, having stacks of a predetermined units of positive electrodes and negative electrodes interposed by the separators, are wound, and so on.
The battery case 200 may have a size to accommodate the electrode assembly 100, and the electrode tabs 10, 11 and the electrode leads 20, 21 which will be described below.
The electrode tabs 10, 11 extend from the electrode assembly 100. For example, the positive electrode tab 10 extends from the positive electrode plate, and the negative electrode tab 11 extends from the negative electrode plate. In this case, when the electrode assembly 100 is configured as a stack of a plurality of positive electrode plates and a plurality of negative electrode plates, the electrode tabs 10, 11 extend from each of the positive electrode plates and negative electrode plates. In this case, the electrode tabs 10, 11 may not be directly exposed to outside the battery case 200, but exposed to outside in a manner of being connected to another constituent element such as electrode leads 20, 21, and so on.
A portion of each of the electrode leads 20, 21 may be electrically connected with the electrode tabs 10, 11 each extending from the positive electrode plate or the negative electrode plate. In this case, the electrode leads 20, 21 may be bonded to the electrode tabs 10, 11 by welding, and so on, which is indicated by the darkened area W in FIG. 1. For example, the method of bonding the electrode leads 20, 21 with the electrode tabs 10, 11 may include general resistance welding, ultrasonic welding, laser welding, riveting, and so on. Further, the electrode leads 20, 21 may additionally include sealing tapes 30, 31 at portions connected to the exposure portions.
In one aspect of a pouch-shaped secondary battery configuration that uses a plurality of positive electrodes and negative electrodes, the positive electrode tabs and negative electrode tabs each extending therefrom are bonded in a generally known manner to be coupled with the electrode leads.
In order to ensure space for bonding portions of the electrode tabs and electrode leads, the electrode assembly is at a predetermined distance apart from the upper part of the battery case.
Meanwhile, when the battery falls or when physical external force is applied on the upper part of the battery, thereby causing the electrode tabs to contact the upper end of the electrode assembly, short circuit is caused at the battery. Generally, the short circuit is caused in many cases due to the contact of the positive electrode tabs with the negative electrode current collector or the negative electrode active material.
Technical constitution wherein insulating member is onto the electrode tab has been suggested in order to solve the problems mentioned above, however, the internal short circuit of the battery is not still prevented completely and problems such as weakened adhesion strength of the insulating member and subsequent detaching thereof exist. Accordingly, improvements are necessary.